In a medium saucepan stir together the sugar, cocoa powder and cinnamon. Slowly whisk in the water and bring the mixture to a boil, once rapid boiling occurs cook an additional 2 minutes. Remove from heat and add the chocolate, let sit 1 minute, then add in the vanilla and stir until smooth. Strain the mixture through a sieve into a large bowl and cool to room temperature, about 45 minutes. Press a layer of plastic wrap over the surface of the chocolate mixture and refrigerate for at least 3 hours. Add the mixture into your ice cream maker and chill for 25-30 minutes, transfer into a freezer safe container and chill for 2-3 hours for a firmer consistency.
Recipe by It Bakes Me Happy at http://itbakesmehappy.com/2012/06/dark-chocolate-sorbet.html